WATER JUNE 2014
78
Technical Papers
speed drive, vertical shaft cantilever
pump installed to recirculate scrubbing
solution from the sump to the scrubber
liquid distribution system.
During the project, several
improvements were realised and
implemented to improve the operability
and robustness of the OCF. Among
them was the addition of feed-forward
control on sodium hypochlorite dosing
to improve performance at high
hydrogen sul de loading and highly
variable inlet conditions. Re nement of
the recirculation and chemical dosing
systems during design also improved
system robustness.
The system also demonstrated
consistently high odour removal
performance; the measured discharge
odour concentration was about 500 OU
and H2S concentrations were below the
measurable range (notionally < 50ppbv),
when inlet H2S concentration ranged
between 1 and 4 ppmv. This compared
to an average measured historical
discharge odour concentration of about
1200 OU and a process guarantee
requirement of less than 1000 OU. Odour
removal performance is also much more
consistent than historical performance,
which varied considerably between
300 and 5000 OU.
The design and implementation
of the odour control facility involved
re-use of existing infrastructure. A staged
construction approach was adopted, with
the existing scrubbers being replaced
in pairs, thereby leaving four scrubbers
online for continued air treatment at
any time. The capital costs of the odour-
related part of the overall project were
about $17m. The operational costs
for the odour treatment facilities are
k$9.1/year per m3/s of foul air treated,
and consist mainly of energy costs for
operating the fans and pumps of the
system and chemicals as the catalyst
for the treatment process (Table 7).
The project was delivered as an alliance.
Table 8 shows the environmental and
social impact performance of the facility,
including the resources required to
operate the system.
Table 9 illustrates the robustness
evaluation for the total odour control
system, including measures to increase
operating reliability. The increase of
robustness due to measures taken
is in this case about 31%.
Figure 3. The odour treatment facility consisting of six chemical scrubbers treating
180m3/s.
Table 8. Environmental and social impact performance for Case Study 3
(a chemical scrubbing system).
Parameter
Unit
Value
Net primary energy usage
kW per 1000m3
0.99
Land occupation
m2 (per m3/s)
9
Water consumption
potable water
kL/year (per m3/s)
65
secondary plant ef uent water
kL/year (per m3/s)
0
Material usage
lter media (replacement every 15 years)
kg/year (per m3/s)
35
chemicals
kg/year (per m3/s)
7867
Atmospheric impact burdens
global-warming burden (CO2 equivalents)
ton/year (per m3/s)
35.8
human-health burden (benzene
equivalents)
g/year (per m3/s)
384
photochemical-ozone burden (ethylene
equivalents)
g/year (per m3/s)
2889
Table 7. Operating costs for Case Study 3 (a chemical scrubbing system).
Parameter
Unit
Value
OPEX costs
Power
k$/year
841
Chemicals
k$/year
552
Water
k$/year
23
Media (incl. disposal of old media)
k$/year
215
Labour
k$/year
56
TOTAL Operating Costs
k$/year
1687
k$/year
(per m3/s)
9.4
ODOUR MANAGEMENT